Printable electronic display

ABSTRACT

A display system includes a substrate upon which the display system is fabricated; a printable electrooptic display material, such as a microencapsulated electrophoretic suspension; electrodes (typically based on a transparent, conductive ink) arranged in an intersecting pattern to allow specific elements or regions of the display material to be addressed; insulating layers, as necessary, deposited by printing; and an array of nonlinear elements that facilitate matrix addressing. The nonlinear devices may include printed, particulate Schottky diodes, particulate PN diodes, particulate varistor material, silicon films formed by chemical reduction, or polymer semiconductor films. All elements of the display system may be deposited using a printing process.

FIELD OF THE INVENTION

The present invention relates to electronic displays, and in particularto non-emissive, flat-panel displays.

BACKGROUND OF THE INVENTION

Electrooptic display systems typically include an electrooptic element(e.g., the display material itself) and electrodes (either opaque ortransparent) for applying control voltages to the electrooptic element.Such a system may also include a nonlinear element to allow formultiplexing of the address lines to the electrodes, and an insulatingmaterial between various layers of the display system. These componentshave been fabricated by a multitude of conventional processes. Forversatility and convenience of manufacture, many recent efforts havefocused on producing all components of such displays by depositionprinting using, for example, screen or ink-jet printing apparatus. Theuse of printing techniques allows displays to be fabricated on a varietyof substrates at low cost.

The conducting materials used for electrodes in display devices havetraditionally been manufactured by commercial deposition processes suchas etching, evaporation, and sputtering onto a substrate. In electronicdisplays it is often necessary to utilize a transparent electrode toensure that the display material can be viewed. Indium tin oxide (ITO),deposited by means of a vacuum-deposition or sputtering process, hasfound widespread acceptance for this purpose. More recently, ITO inkshave been deposited using a printing process (see, e.g., U.S. Pat. No.5,421,926).

For rear electrodes (i.e., the electrodes other than those through whichthe display is viewed) it is often not necessary to utilize transparentconductors. Such electrodes can therefore be formed from a material suchas a silver ink. Again, these materials have traditionally been appliedusing costly sputtering or vacuum deposition methods.

Nonlinear elements, which facilitate matrix addressing, are an essentialpart of many display systems. For a display of M×N pixels, it isdesirable to use a multiplexed addressing scheme whereby M columnelectrodes and N row electrodes are patterned orthogonally with respectto each other. Such a scheme requires only M+N address lines (as opposedto M×N lines for a direct-address system requiring a separate addressline for each pixel). The use of matrix addressing results insignificant savings in terms of power consumption and cost ofmanufacture. As a practical matter, its feasibility usually hinges uponthe presence of a nonlinearity in an associated device. The nonlinearityeliminates crosstalk between electrodes and provides a thresholdingfunction. A traditional way of introducing nonlinearity into displayshas been to use a backplane having components that exhibit a nonlinearcurrent/voltage relationship. Examples of such devices used in displaysinclude thin-film transistors (TFT) and metal-insulator-metal (MIM)diodes. While these types of devices achieve the desired result, bothinvolve thin-film processes. Thus they suffer from high production costas well as relatively poor manufacturing yields.

Another nonlinear system, which has been used in conjunction with liquidcrystal displays, a printed varistor backplane (see, e.g., U.S. Pat.Nos. 5,070,326; 5,066,105; 5,250,932; and 5,128,785, hereafter the“Yoshimoto patents,” the entire disclosures of which are herebyincorporated by reference). A varistor is a device having a nonlinearcurrent/voltage relationship. Ordinarily, varistors are produced bypressing various metal-oxide powders followed by sintering. Theresulting material can be pulverized into particulate matter, which canthen be dispersed in a binder.

Additionally, the prior art mentions the use of a varistor backplane toprovide thresholding for a nonemissive electrophoretic display device;see Chiang, “A High Speed Electrophoretic Matrix Display,” SID 1980Technical Digest. The disclosed approach requires the deposition of thedisplay material into an evacuated cavity on a substrate-borne,nonprinted varistor wafer. Thus, fabrication is relatively complex andcostly.

Some success has been achieved in fabricating electronic displays usingprinting processes exclusively. These displays, however, have for themost part been emissive in nature (such as electroluminescent displays).As is well known, emissive displays exhibit high power-consumptionlevels. Efforts devoted to nonemissive displays generally have notprovided for thresholding to facilitate matrix addressing.

DESCRIPTION OF THE INVENTION BRIEF SUMMARY OF THE INVENTION

The present invention facilitates fabrication of an entire nonemissive(reflective), electronically addressable display using printingtechniques. In particular, printing processes can be used to deposit theelectrodes, insulating material, the display itself, and an array ofnonlinear devices to facilitate addressing. Accordingly, fabrication ofthe displays of the present invention may be accomplished atsignificantly lower cost and with far less complexity than would obtainusing coventional fabrication technologies. Furthermore, the approach ofthe present invention affords greater versatility in fabrication,allowing the displays to be applied to substrates of arbitraryflexibility and thickness (ranging, for example, from polymericmaterials to paper). For example, static screen-printed displays may beused in signs or lettering on consumer products; the invention can alsobe used to form dynamic, electronically alterable displays. Moreover,the invention can be employed to produce flat-panel displays atmanufacturing costs well below those associated with traditional devices(e.g., liquid crystal displays).

As used herein, the term “printing” connotes a non-vacuum depositionprocess capable of creating a pattern. Examples include screen printing,ink-jet printing, and contact processes such as lithographic and gravureprinting.

For the display element, the present invention utilizes certainparticle-based nonemissive systems such as encapsulated electrophoreticdisplays (in which particles migrate within a dielectric fluid under theinfluence of an electric field), electrically or magnetically drivenrotating-ball displays (see, e.g., U.S. Pat. Nos. 5,604,027 and4,419,383), and encapsulated displays based on micromagnetic orelectrostatic particles (see, e.g., U.S. Pat. Nos. 4,211,668; 5,057,363and 3,683,382). A preferred approach is based on discrete,microencapsulated electrophoretic elements, suitable examples of whichare disclosed in U.S. application Ser. No. 08/738,260 and PCTapplication serial no. US96/13469. The entire disclosures of the '027,'383, '668, '363, and '382 patents, as well as the '260 and '469applications, are hereby incorporated by reference.

Electrophoretic displays in accordance with the '260 application arebased on microcapsules each having therein an electrophoreticcomposition of a dielectric fluid and a suspension of particles thatvisually contrast with the dielectric liquid and also exhibit surfacecharges. A pair of electrodes, at least one of which is visuallytransparent, covers opposite sides of a two-dimensional arrangement ofsuch microcapsules. A potential difference between the two electrodescauses the particles to migrate toward one of the electrodes, therebyaltering what is seen through the transparent electrode. When attractedto this electrode, the particles are visible and their colorpredominates; when they are attracted to the opposite electrode,however, the particles are obscured by the dielectric liquid.

In accordance with the present invention, the electrophoreticmicrocapsules are suspended in a carrier material that may be depositedusing a printing process. The suspension thereby functions as aprintable electrophoretic ink. Preferably, the electrodes are alsoapplied using a printing process. For example, the transparentelectrode(s) may be a print-deposited ITO composition, as described inthe above-mentioned '926 patent, and the rear electrodes may also be anITO composition or, alternatively, a silver ink. The electrophoretic inkis deposited between the electrode arrays, forming a sandwich structure.

Preferably, the invention also includes a series of nonlinear devicesthat facilitate matrix addressing, whiereby M×N pixels are address withM+N electrodes; again, these devices (which may include diodes,transistors, varistors or some combination) are desirably applied byprinting. In one approach, a varistor backplane is deposited inaccordance with, for example, the Yoshimoto patents described above.Alternatively, a backplane of nonlinear devices may utilize printedparticulate silicon diodes as taught, for example, in U.S. Pat. No.4,947,219 (the entire disclosure of which is hereby incorporated byreference). With this approach, a particulate doped silicon is dispersedin a binder and applied in layers to produce diode structures.

Thus, a display system in accordance with the invention may include asubstrate upon which the display system is fabricated; a printableelectrooptic display material, such as a microencapsulatedelectrophoretic suspension; printable electrodes (typically based on atransparent, conductive ink) arranged in an intersecting pattern toallow specific elements or regions of the display material to beaddressed; insulating layers, as necessary, deposited by printing; andan array of nonlinear elements that facilitate matrix addressing. Thenonlinear devices may include printed, particulate Schottky diodes,particulate PN diodes, particulate varistor material, silicon filmsformed by chemical reduction, or polymer semiconductor films.

The displays of the present invention exhibit low power consumption, andare economically fabricated. If a bistable display material is used,refreshing of the display is not required and further power consumptionis achieved. Because all of the components of the display are printed,it is possible to create flat-panel displays on very thin and flexiblesubstrates.

In another aspect, the invention comprises means for remotely powering anonemissive display, and in still another aspect, the inventioncomprises a graduated scale comprising a series of nonemissive displayseach associated with a nonlinear element having a different breakdownvoltage.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing discussion will be understood more readily from thefollowing detailed description of the invention, when taken inconjunction with the accompanying drawings, in which:

FIG. 1 schematically represents a display in accordance with the presentinvention, including row and column electrodes, an electrooptic displaymaterial, and an array of nonlinear elements;

FIG. 2 is a graph of the current/voltage characteristic of a printablenonlinear element in accordance with the invention;

FIG. 3A is an enlarged sectional view of a varistor device in accordancewith the invention;

FIG. 3B is an enlarged sectional view of a semiconductor Schottky diodein accordance with the invention;

FIG. 3C is an enlarged sectional view of a particulate semiconductordiode in accordance with the invention;

FIGS. 4A and 4C are enlarged sectional views of display systems inaccordance with the invention each including row and column electrodes,a microencapsulated electrophoretic display material, an insulatormaterial, and a nonlinear backplane;

FIGS. 4B and 4D are partially cutaway plan views of the display systemsshown in FIGS. 4A and 4C, respectively;

FIG. 5 is an isometric view of a display device in accordance with theinvention, and which has been fabricated into the form of the letter M;and

FIG. 6A is a partially exploded, schematic illustration of an addressconfiguration with one electrode floating;

FIG. 6B is an elevation of an alternative embodiment of thefloating-electrode address configuration shown in FIG. 6A;

FIGS. 7A and 7B schematically illustrate remotely powered displays; and

FIGS. 8A and 8B illustrate application of the invention to produce agraduated scale.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Refer first to FIG. 1, which schematically illustrates a display systemin accordance with the invention. The depicted system includes anelectrophoretic display, and the various components are deposited by aprinting process as permitted by the present invention. It should beunderstood, however, that the invention may be practiced using otherparticle-based displays, and with components deposited by conventional(e.g., vacuum-type) processes.

The illustrated embodiment includes a series of row and columnelectrodes indicated generally at 100 and 102, respectively, andpreferably formed using a printed conductive ink. Assuming the columnelectrodes 100 are the ones through which the display is viewed, theseare transparent. The row electrodes 102, which serve as the rearelectrodes, may or may not be transparent, depending upon theapplication. The electrophoretic display material 104 and the nonlinearelements 106 are sandwiched between column electrodes 100 and rowelectrodes 102, forming a series circuit at each topological point ofoverlap (intersection) between the two electrode arrays. The displayelement 104 is shown as a capacitor because, for most displayapplications, the display material acts as a dielectric between twoconductive plates (the electrodes), essentially forming a capacitor. Thenonlinear element 106 is depicted as two back-to-back diodes because theI-V characteristic of element 106 is preferably similar thereto.

The display shown in FIG, 1 may be addressed by any of a variety ofschemes. Assume, for purposes of discussion, that the voltage across adisplay pixel 104 and the associated nonlinear element 106 is defined asthe row voltage (V_(r)) minus the column voltage (V_(c)). Assume furtherthat the display material is configured to “switch” or change state if acertain voltage V_(on) or greater is applied to it, and to reassume theoriginal state when a voltage of −V_(on) is applied across it. Thevoltage V_(on) is a function of the display material and the desiredswitching speed.

In a matrix addressing scheme it possible to selectively apply voltageof V_(on) or −V_(on) to certain pixels using row-at-a-time addressing,but unselected pixels may experience a voltage of up to V_(on)/2 inmagnitude. This half-select voltage V_(h) is the reason that a thresholdis required. By placing a nonlinear element 106 in series with thedisplay material, interference (e.g., slow but nonetheless perceptibleswitching) due to V_(h) is eliminated. The nonlinear element 106 ischosen such that for voltages of less than V_(h) across it, very littlecurrent flows. When the voltage across nonlinear element 106 rises toV_(on), however, the device effectively acts as a smaller resistance,allowing more current to flow. This prevents “half-selected” pixels fromswitching while ensuring that fully selected ones do switch. It is thusnecessary to have a nonlinear device with symmetrical characteristicssuch that V_(b), the breakdown voltage of the device, is greater thanV_(h), but less than V_(on). The amount of current that the devicepasses at V_(on) determines the switching speed of the display; that is,the amount of current passed at V_(h) determines how long it will takean unselected pixel to switch, and thus in non-bistable systemseffectively determines how many pixels can be multiplexed (by dictatinghow often the display must be refreshed for a given switching speed).

A preferred current/voltage characteristic of the nonlinear element 106is depicted at 200 in FIG. 2. The characteristic is preferably symmetricas shown, with high impedance between some breakdown voltages −V_(b) andV_(b). For voltages greater in magnitude than V_(b) the device exhibitsa lower impedance, allowing exponentially more current to flow as themagnitude of the voltage across the device increases. The device whoseresponse is depicted in FIG. 2 is essentially equivalent to twoback-to-back Zener diodes. (Two diodes are necessary to ensure that thedevice is symmetric.) However, the response profile 200 can be obtainedusing devices other than back-to-back Zener diodes. The voltage V_(b) isequal to the forward voltage drop V_(f) of one diode plus the reversebreakdown voltage V_(br) of the second diode. V_(br) is usually largerin magnitude than V_(f) and thus accounts for most of the breakdownvoltage. Above V_(b), current flow is exponentially proportional to theapplied voltage.

This is similar to a varistor. A varistor has an inherently symmetricalI-V curve, given by the relation I_(v)=(V/K)^(α) where V is the appliedvoltage, K is a constant and α is determined by device structure. Thus,the varistor also offers an exponential rise in current for voltagesabove some breakdown voltage, and while the actual IV curves ofback-to-back diodes and varistors may be slightly different, they havethe same general properties and are both suitable for use as nonlinearelements in the display system of the present invention.

Methods for creating nonlinear elements 106 vary depending upon thedesired implementation. FIGS. 3A–3C show cross-sections of threedifferent nonlinear elements suitable for use herewith: a particulatevaristor device, a particulate Schottky diode, and a particulate PNdiode.

The varistor of FIG. 3A can be prepared in the following manner (inrough accordance with the Yoshimoto patents). ZnO particles are firstpressed under high pressure (greater than 100 kg/cm). After pressing,the resulting ZnO pellets are sintered at a temperature between 800° C.and 1400° C. After the initial sintering the ZnO is pulverized andsintered again. In order to fabricate a good varistor, the resultingparticles are doped with one or more compounds selected from the groupconsisting of Sb₂O₃, MnO, MnO₂, CO₂O₃, CoO, Bi₂O₃, and Cr₂O₃. The amountof these dopants is up to 15% by weight of the ZnO particles. Thismixture is then sintered again at temperatures greater than 800° C. Thefinal particles are depicted at 300 in FIG. 3A.

The particles 300 are mixed with a suitable binder for screen printing.Binders based on either ethyl cellulose or polyvinyl alcohol withsuitable solvents, as are well known to those of skill in the art, maybe used. For ethyl cellulose-based binders, butyl carbitol acetate isthe preferred solvent. The binder is typically almost completely burnedoff after curing, but is represented schematically (pre-cure) at 302.

In addition to the aforementioned binder it is desirable to add a glassfrit to the mixture to provide for adhesion of the varistor paste to thesubstrate onto which it is to be printed. Typically, a glass frit havinga low-temperature (e.g., ˜400° C.) melting point is used. An alternativeto the binder/glass-frit mixture is to disperse the varistor particlesin a photohardening resin or epoxy. This provides adhesion the particlesat a lower temperature than is required by the glass frit, and is curedthrough exposure to actinic radiation.

The exact composition of the mixture may vary. In a typical application,the composition may consist of 70% varistor material, 20% glass frit and10% binder.

Different ratios may be used, for example, depending on whether thebinder is ethyl cellulose-based, polyvinyl alcohol-based, resin-based,or epoxy-based. This slurry or paste formed by dispersion of theparticles in the binder is then deposited by means of standard printingtechniques onto the bottom electrode 304.

The deposited mixture is cured at temperatures up to 400° C. and/orexposed to actinic radiation, depending on the nature of the binder.Binders including a glass frit typically require curing temperatures of400° C. and higher, while the systems not including glass may be curedat lower temperatures (e.g., less than 200° C.). After curing of thevaristor, a top electrode 306 is printed, thus completing the device.

The Schottky diode structure shown in FIG. 3B is prepared in thefollowing manner, in rough accordance with the '21 g patent. Siliconparticles derived from either amorphous or single-crystal silicon arefirst obtained. In an exemplary embodiment, P-type (boron-doped) siliconis employed. A suitable material is chosen for the rear electrode suchthat an ohmic contact can be formed with the semiconductor. Aluminum isespecially suitable, although other metals with appropriate electronwork functions may be used instead.

A rear or bottom electrode 320 is first printed and cured. The siliconparticles 322 are mixed in a suitable binder 324 to produce a pastehaving desired properties for the particular application. For example,ethyl cellulose with butyl carbitol actetate as a solvent can serve as asuitable binder. For adhesion purposes, a glass frit may be mixed inwith the binder and the silicon particles. The mixture is first printed(e.g., screened) onto the rear electrode. It is desirable to limit thethickness of this printed layer so that it is comparable to the diameterof the silicon particles. This produces a monolayer of particles, whichensures good current flow between the electrodes.

The applied mixture is then exposed to a multiphase temperature cycle.Initially a low temperature of 200° C. is used to burn off the organicbinder. The sample is then raised to a temperature of approximately 660°C. This temperature, which is the eutectic point of silicon andaluminum, allows the silicon particles to form a good ohmic contact tothe electrode. (Of course, the temperature may be altered if a materialother than aluminum is used for rear electrode 320.) At this temperaturethe glass fit also becomes molten, helping to adhere the silicon toelectrode 320 as well as providing an insulating layer so that the topelectrode 326 does not short to bottom electrode 320. The temperature isthen slowly lowered, allowing the silicon to recrystallize. After thesample has been cooled, top electrode 326 is printed on the device.Silver inks provide rectifying contacts to P-type materials and arepreferred for electrode 326 in the context of this example. Differentmaterials may be utilized if desired, or if N-type particles are used.After the electrode 326 is printed, the sample is fired to cure the inkand complete the device.

The device depicted in FIG. 3B forms only one half of the necessaryback-to-back structure. A second device is therefore created andattached in the appropriate configuration to the first device to producea symmetric nonlinear element.

The PN diode structure shown in FIG. 3C may be prepared as follows.Silicon particles derived from either amorphous or single-crystalsilicon are first obtained. In a representative example, P-type andN-type silicon are used. A suitable material is chosen for both the rearand front electrodes such that ohmic contacts can be formed with the twotypes of semiconductor. The bottom electrode 330 is first printed andcured. The P-type silicon particles 332 are once again mixed in asuitable binder 334. Once again, a variety of pastes may be obtained,depending on the binder chosen. Ethyl cellulose with butyl carbitolacetate as the solvent can serve as a suitable binder. For adhesionpurposes, a glass frit may be mixed in with the binder and silicon. Themixture is printed (e.g., by screening) onto electrode 330, which servesas the rear electrode.

The N-type particles 336 are also dispersed in a binder. After theP-type particles are exposed to a 200° C. temperature cycyle to burn offtheir binder, the N-type particles are printed (again, for example, byscreening) on top of the layer of P-type particles 332. Once again, a200° C. temperature cycle is used to burn off the binder. A topelectrode 338 is then printed on the N particles.

This construction is then exposed to a multiphase temperature cycle.Initially a low temperature of 200° C. is used to eliminate anyremaining organic binder. The sample is then raised to a highertemperature, which is chosen to alloy the silicon particles to theirrespective contacts. At this temperature the glass frit also becomesmolten, helping to adhere the silicon to the contact as well asproviding an insulating layer so that the elctrodes do not short to eachother. The temperature is then slowly lowered, allowing the silicon torecrystallize and thereby form the PN diode structure.

Once again, this device only forms one half of the necessaryback-to-back structure. A second device is therefore created andattached in the appropriate configuration to the first device to producea symmetric nonlinear element.

It is also possible to utilize for creating printable nonlinear elementsthat do not involve particulate systems. For example, the printablenonlinear element may be a silicon film formed by chemically reducing amolecularly dissolved silicide salt, as described in the '469 PCTapplication and in Anderson et al., “Solution Grown Polysilicon for FlatPanel Displays,” Mat. Res. Soc. Meet., Spring 1996 (paper H8.1)(incorporated by reference herein); or may instead be a printablepolymer conductor, as described in the '469 PCT application and in Torsiet al., “Organic Thin-Film Trasnsistors with High On/Off Ratios,” Mat.Res. Soc. Symp. Proc. 377:695 (1995) (incorporated by reference herein).

The electrooptic display element of the present invention is preferablyan electrophoretic display in accordance with the '260 application, andis based on an arrangement of microscopic containers or microcapsules,each microcapsule having therein an electrophoretic composition of adielectric fluid and a suspension of particles that visually contrastwith the dielectric liquid and also exhibit surface charges. Electrodesdisposed on and covering opposite sides of the microcapsule arrangement,provide means for creating a potential difference that causes theparticles to migrate toward one of the electrodes.

As discussed in the '260 application, the display microcapsulespreferably have dimensions ranging from 5 to 500 μm, and ideally from 25to 250 μm. The walls of the microcapsules preferably exhibit aresistivity similar to that of the dielectric liquid therein. It mayalso be useful to match the refractive index of the microcapsules withthat of the electrophoretic composition. Ordinarily, the dielectricliquid is hydrophobic, and techniques for encapsulating a hydrophobicinternal phase are well characterized in the art. The process selectedmay impose limitations on the identity and properties of the dielectricliquid; for example, certain condensation processes may requiredielectric liquids with relatively high boiling points and low vaporpressures.

FIGS. 4A and 4B illustrate a complete printed display system with acontinuous nonlinear-element backplane. The device includes a substrate400, which is typically a thin, flexible material such as KAPTON film.The row electrodes 402 have preferably been deposited on substrate 400by means of a printing process. In the illustrated embodiment, thenonlinear backplane 404 is a continuous layer of either particulatevaristor material or particulate diode material. The structurerepresented at 404 may also be a layer of particulate silicon, a printedmetal contact and then another layer of particulate silicon.Alternatively, the structure 404 may comprise layers of P- and N-dopedparticulate semiconductor inks, printed in an ascending pattern such asPNPNPNNPNPNP. An arbitrarily large number of layers may be printed, theoptimal number depending primarily upon the desired breakdown voltage.

An optional second set of printed row electrodes 406 (shown only in FIG.4A), aligned with the first set 402, provide a contact to the other sideof the nonlinear material 404. An insulator material, such as AchesonML25208, is print-deposited in the lanes 408 defining the space betweenelectrodes 402, so that a smooth surface is formed. An electroopticdisplay 410, such as a layer of electrophoretic display microcapsules,is print-deposited onto electrodes 406 or, if these are omitted, ontononlinear backplane 404. A set of transparent column electrodes 412 isprint-deposited onto display 410 in a pattern orthogonal to rowelectrodes 402 (and, if included, 406). An insulator material isprint-deposited in lanes 414 between electrodes 412. Active pictureelements are defined in the regions of display 410 where theseorthogonal sets of electrodes overlap. Thus, a display with M rowelectrodes and N column electrodes has M×N picture elements.

The material of nonlinear backplane 404 can be continuous or depositedas a discrete array, e.g., in a matrix pattern with nonlinear materialprinted only in the areas of active picture elements (i.e., where rowand column electrodes overlap). Such an arrangement is depicted in FIGS.4C and 4D. A substrate 430, typically composed of a thin, flexiblematerial such as KAPTON film, underlies a set of row electrodes 432which preferably have been deposited on the substrate by means of aprinting process. The nonlinear backplane 434, which may compriseprinted back-to-back diodes or printed varistor material, is depositedin a pattern corresponding to the active picture elements—that is, wherethe row and column electrodes cross. An insulator material 435 isdeposited so as to surround elements 434 and thereby create a uniformplanar surface. Once again, the structure represented at 434 may also bea layer of particulate silicon, a printed metal contact and then anotherlayer of particulate silicon. Alternatively, the structure 434 maycomprise layers of P- and N-doped particulate semiconductor inks,printed in an ascending pattern such as PNPNPNNPNPNP. An arbitrarilylarge number of layers may be printed, the optimal number dependingprimarily upon the desired breakdown voltage.

An optional second set of printed row electrodes 436, aligned with thefirst set 432, provide a contact to the other side of the nonlinearmaterial 434. An insulator material, such as Acheson ML25208, isprint-deposited in the lanes 438 defining the space between electrodes432. An electrooptic display 440 is print-deposited onto electrodes 436or, if these are omitted, onto nonlinear backplane 434. A set oftransparent column electrodes 444 is print-deposited onto display 440 ina pattern orthogonal to row electrodes 432 (and, if included, 436).Active picture elements are defined in the regions of display 440 wherethese orthogonal sets of electrodes overlap. An insulator material isprint-deposited in lanes 4446 between electrodes 444.

FIG. 5 depicts a screen-printed display 500 in the form of the letter‘M’. The display 500 is a layered structure, the layers corresponding tothose shown sectionally in FIGS. 4A and 4B. The result is a nonemissive,screen-printed, microencapsulated electrophoretic display, printed on anarbitrary substrate in an arbitrary shape.

FIGS. 6A and 6B show a scheme for addressing a display where the topelectrode is “floating,” i.e., not electrically connected. This greatlysimplifies the layout, although at the cost of increasing the requiredsupply voltage; the depicted arrangement also envisions pixelwiseaddressing. With reference to FIG. 6A, a series of display elements 602each overlie an associated electrode 604, all of which are carried as apixel array on a substrate 606. A single floating plate electrode 608overlies the displays 602. Alternatively, as shown in FIG. 6B, thedisplay may be a continuous element substantially coextensive withsubstrate 606; discrete regions of such a display, which lie above andare separately addressed by each of the electrodes 604, act asindividual pixels.

Electrodes 604 are spaced apart from one another by a distance s, andwith the components in place, are separated from electrode 608 by adistance r. So long as r<<s, placing two adjacent electrodes 604 at V₁and V₂ induces a potential of (V₁+V₂)/2 at electrode 608; accordingly,as a result of the arrangement, the field across display medium 602 willbe half that which would be achieved were V₁ and V₂ applied directly.More specifically, suppose, as shown in FIG. 6B, that a first electrode604 ₁ is grounded and a second electrode 604 ₂ connected to a battery620 of voltage V. In this case the induced voltage in electrode 608 isV/2, but the electric field F traverses the display 605 in oppositedirections above electrodes 604 ₁, 604 ₂. As a result, assuming that thevoltage V/2 is sufficient to cause switching of display 625 within anacceptable switching time, the regions of display 625 above the twoelectrodes will be driven into opposite states.

This arrangement cannot sustain a condition where every display element(or region) is in the same state. To provide for this possibility, aseparate electrode 650 (and, if the display is organized discretely, acorresponding display element 652) are located outside the visual areaof the display—that is, the area of the display visible to the viewer.In this way, electrode 650 may be biased oppositely with respect to allother pixels in the device without visual effect.

Refer now to FIGS. 7A and 7B, which illustrate remote powering ofdisplays. With particular reference to FIG. 7A, a capacitive arrangementcomprises a logic/control unit 700 and a pair of transmitting electrodes710 connected thereto. A display unit or “tag” 720, which may have anonlinear backplane, is connected to a complementary pair of receivingelectrodes 730. Upon application of an AC signal to transmittingelectrodes 710, an AC field is induced in receiving electrodes 720 asthey physically approach the transmitting electrodes. The currentproduced by this field can be used to directly power display unit 720(e.g., after being passed through a rectifier), or it can instead befiltered or otherwise processed by on-board logic in display 720. Forexample, the AC signal can convey information to such display logic todetermine the appearance of the display. For example, one or more notchfilters can be employed so that upon detection of a first AC frequency,the display 720 is placed into a certain state, and upon detection of asecond AC frequency, is changed into a different state. With theaddition of nonlinear elements, more sophistical signal processing canbe effected while retaining the simple circuit design of FIG. 7A. Allelectronic elements associated with logic unit 700 and display unit 720may be generated by a printing process.

FIG. 7B shows an inductive approach to remote powering and signalling.The illustrated inductive arrangement includes a logic/control unit 740and one or more transmitting coils 750. A display unit or tag 770, whichmay have a nonlinear backplane, is connected to a complementary pair ofreceiving coils 760. Upon application of an AC signal to transmittingcoils 750, the resulting magnetic field induces an AC current inreceiving coils 760. The induced current can be used to directly powerdisplay unit 770 or convey information in the manner described above.Once again, the arrangment may include notch filters or additionalnonlinear elements for more sophistical signal processing. Allelectronic elements associated with logic unit 740 and display unit 770may be generated by a printing process.

Refer now to FIGS. 8A and 8B, which illustrate application of theinvention to create a voltage scale (which may serve, for example, as abattery indicator). The display system 800 includes a series ofindividual particle-based (preferably electrophoretic) display devices810 mounted on a substrate 820. Each display device 810 includes a rearelectrode, a nonlinear device, a display element (which may be discreteor shared among all devices 810), and a transparent electrode; thesecomponents are preferably printed in a stack structure in the mannerillustrated in FIG. 6A.

As shown in FIG. 8B, each display can be represented as a nonlineardevice 830 ₁ . . . 830 _(n) and a capacitor 840 ₁ . . . 840 _(n). Thenonlinear devices 830 have progressively higher breakdown voltages.Accordingly, the number of such displays “turned on” (or “turned off”)at any time reflects the voltage (e.g., from a battery 850) across thedisplays. In operation, all of the displays 810 are initially in thesame state. Each of the displays 810 changes state only when thepotential exceeds the breakdown voltage of the associated nonlineardevice. To reset the device, the user activates a switch (not shown)which reverses the connection of battery 850 and causes it to generate apotential exceeding the breakdown voltages of all nonlinear devices 830.

It will therefore be seen that the foregoing represents a versatile andconvenient approach to the design and manufacture of particle-baseddisplay systems. The terms and expressions employed herein are used asterms of description and not of limitation, and there is no intention,in the use of such terms and expressions, of excluding any equivalentsof the features shown and described or portions thereof, but it isrecognized that various modifications are possible within the scope ofthe invention claimed.

1. A printable electronic display comprising: a. a first set of displayelectrodes associated with a first layer; b. a second set of displayelectrodes associated with a second layer distinct from the first layerand disposed in an intersecting pattern with respect to the first set ofelectrodes, the first and second sets of electrodes not contacting oneanother; c. a particle-based, nonemissive display; and d. a plurality ofnonlinear elements, the display and the nonlinear elements beingsandwiched between the first and second display electrode layers so asto electrically couple at least some electrodes of the first layer withcorresponding electrodes of the second layer at regions of intersectionand thereby facilitate actuation of the display by the electrodes atsaid regions.
 2. The display system of claim 1 wherein the nonemissivedisplay is an electrophoretic display.
 3. The display system of claim 1wherein the nonemissive display is a rotating-ball display.
 4. Thedisplay system of claim 1 wherein the nonemissive display is anelectrostatic display.
 5. The display system of claim 1 furthercomprising a thin, flexible substrate.
 6. The display system of claim 1wherein the first and second sets of electrodes are each arranged in aplanar configuration, the electrodes of the first set being orthogonalto the electrodes of the second set.
 7. The display system of claim 6wherein the electrophoretic display material and the nonlinear elementsare arranged in planar form and sandwiched between the first and secondsets of electrodes.
 8. The display system of claim 1 wherein theelectrophoretic display comprises a plurality of discrete,microencapsulated electrophoretic display elements.
 9. The displaysystem of claim 8 wherein the electrophoretic display comprises: a. anarrangement of discrete microscopic containers, each container being nolonger than 500 μm along any dimension thereof; and b. within eachcontainer, a dielectric fluid and a suspension therein of particlesexhibiting surface charges, the fluid and the particles contrastingvisually, the particles migrating toward one of the sets of electrodesin response to a potential difference therebetween.
 10. The displaysystem of claim 1 wherein the first and second sets of electrodes areprintable, at least one of the sets of electrodes being visuallytransparent.
 11. The display system of claim 1 wherein the nonlinearelements are printable.
 12. The display system of claim 1 wherein theelectrophoretic display is printable.
 13. The display system of claim 11wherein the nonlinear elements are a print-deposited ink exhibiting anonlinear electrical characteristic.
 14. The display system of claim 13wherein the ink comprises: a. a binder for printing; and b. ZnOparticles doped with at least one compound selected from the groupconsisting of sintered ZnO, Sb₂O₃, MnO, MnO₂, CO₂O₃, CoO, Bi₂O₃ andCr₂O₃.
 15. The display system of claim 14 wherein the binder comprisesethyl cellulose and butyl carbitol.
 16. The display system of claim 15wherein the binder further comprises a glass frit.
 17. The displaysystem of claim 15 wherein the binder comprises an epoxy resin.
 18. Thedisplay system of claim 15 wherein the binder comprises aphotohardenable resin.
 19. The display system of claim 13 wherein theink comprises: a. a binder for printing; and b. a doped, particulatesilicon.
 20. The display system of claim 19 wherein the binder comprisesethyl cellulose and butyl carbitol.
 21. The display system of claim 19wherein the binder further comprises a glass frit.
 22. The displaysystem of claim 19 wherein the binder comprises an epoxy resin.
 23. Thedisplay system of claim 19 wherein the binder comprises aphotohardenable resin.
 24. The display system of claim 1 wherein theelectrodes comprise a print-deposited conductive ink.
 25. The displaysystem of claim 19 wherein the electrodes comprise a print-depositedconductive ink providing a rectifying contact to the silicon.
 26. Thedisplay system of claim 24 wherein the ink is transparent.
 27. Thedisplay system of claim 24 wherein the ink comprises indium tin oxide.28. The display system of claim 1 wherein each set of electrodes isarranged in lanes with spaces therebetween, and further comprising aninsulating material located in the spaces.
 29. The display system ofclaim 1 wherein the nonlinear elements comprise Schottky diodes.
 30. Thedisplay system of claim 1 wherein the nonlinear elements comprise PNdiodes.
 31. The display system of claim 1 wherein the nonlinear elementscomprise varistors.
 32. The display system of claim 1 wherein thenonlinear elements comprise silicon films formed from silicide salt. 33.The display system of claim 1 wherein the nonlinear elements comprise apolymer conductor.